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Today the Taiwan D-Link support give me the fix for the ipv6 problem.
Thank you for everything. I will contact D-Link and I will let you know how it went.
On the official page of D-Link I found this new official beta firmware that solved my problem with the IPV6.The file is: FW for IPv6 1.20beta03and the link is on the official D-Link support page:https://eu.dlink.com/ro/ro/products/dir-878-exo-ac1900-mumimo-wifi-routerNow the router works very well on IPV6 with RCS/RDS provider.Thank you for everything.